This invention was made in the course of, or under, a contract with the Energy Research and Development Administration. The invention relates generally to methods for fabricating tubular metal articles, such as transitions, diffusers, and flow nozzles. More particularly, it relates to the fabrication of leak-tight tubular articles whose internal dimensions are highly critical, the articles being composed of a metal which tends to warp if fusion-bonded, as by arc welding or gas welding. As used herein, the term "metal" includes metals and metal alloys. The term "welded" as used herein includes brazing.
In the fabrication of certain high-precision apparatus, the need arose for a tapered metal flow channel, or nozzle, for conveying gaseous uranium hexafluoride. Specifications called for the nozzle to be leak-tight, to be composed of relatively thin metal compatible with UF.sub.6, and to have an internal configuration corresponding very closely to design. A conventional method for fabricating such a nozzle would be to (a) form separate subsections of the nozzle, (b) contour the interior of each subsection by a highly precise technique, and (c) weld the subsections together to provide a leak-tight assembly. Unfortunately, that approach is not satisfactory because the amount of welding required causes the metal to expand appreciably and then distort upon cooling. Another conventional approach is to fabricate a tubular metal housing by standard techniques and then very precisely mount contoured inserts in the housing to define the desired flow channel. That approach is both tedious and costly.